Following the destruction of the Chimera's central tower in London and their armies eradicated throughout Britain in the Battle of London, humanity was made aware that the Chimeran tower network was the key source of the Chimera's vulnerability as their survival were dependent on the Angels who mainly inhabited the towers. The Maquis, an European mainland resistance movement, approached the British for a joint-planned operation to repeat the same liberation in Britain by destroying the Chimera's hub tower in Paris, France and thereby eradicating the Chimera from Western Europe. However, the operation was not only to destroy the Paris central tower, but also using an experimental serum created by Dr. Claude Bouchard that would eradicate the Chimera's Carrier strain, which were tasked in transporting Chimeran virus-infected humans to conversion centers, and thus grounding the Chimera's conversion process to a halt.
Similar to Operation Deliverance, the British military would be inserted into the European continent and assist the Maquis in destroying the Paris tower and causing the meltdown of the tower network across Western Europe. The British Intelligence Corps would dispatch two squadrons of British forces to aid the Maquis. The First Squadron under the command of Major Stephen Cartwright would fly first into Rotterdam, in which it is one of the few open corridors to bypass the Chimera's coastal fortifications, follow four hours later by the Second Squadron under Colonel Rachel Parker. Accompanied by the Maquis, the British would cross Chimera lines into Luxembourg where the Maquis stronghold lies, and then from there preparing their attack on the Paris tower.
In the early phase of the operation, the Maquis made a major intelligence error in regarding to the Chimera's coastal defenses. Since the Chimera's occupation of Europe, the Chimera constructed massive fortifications on the coastlines of Western Europe and making it almost impossible to penetrate through. The Chimera, however, hastily erected three gun towers in Rotterdam that came unnoticed for the Maquis. The Maquis's Intel scouts in the city had tried to warn the British about the gun towers via radio, but their broadcasts never reached England as the Chimera had started jamming signals from the gun towers. Major Cartwright's First Squadron suffered heavy casualties from the gun towers.
Despite the losses, human forces were able to disable the gun towers and allowing Parker's Second Squadron to safely arrive, bringing supplies and reinforcements to a makeshift command center outside of Rotterdam. Allied leaders then hastily drawn up plans and assignments; Cartwright was later led a task force to intercept Chimeran Earth Movers in Gerolstein that were heading for Luxembourg while Parker took the remainder of the Second Squadron to Luxembourg to finalize plans for the assault on the Paris tower.
During this time, British mercenary James Grayson, Colonel Roland Mallery, and Lieutenant Raine Bouchard investigated a new type of conversion facility in Bonn, Germany. The group were separated, with Bouchard captured by the Chimera and falling into the initial stages of the conversion process, but Grayson was able to rescue her, believing her to be yet uninfected, and then destroying the facility.
On September 2, Major Cartwright faced complications in stopping the Chimeran Earth Movers in Gerolstein. James Grayson aided Cartwright in immobilizing the Earth Movers, but their victory was overshadowed by an all-out Chimeran assault on the Maquis Fortress after the Chimera were alerted to the Maquis presence in Luxembourg.
The Chimera surrounded the Maquis headquarters, as their war machines and drones cut off the humans' escape routes, and forcing the British and Maquis to use their last VTOLs to evacuate the refugees to the Maquis' last remaining safe zone in Reims. Dr. Claude Bouchard along with his daughter Raine were still occupied in developing a anti-Carrier serum, in which Raine had deliberately allowed herself to being infected in Bonn to allow her father to gain a sample of the Chimeran virus. British and Maquis soldiers defended the fortress long enough to evacuate the refugees and enough time for Dr. Bouchard and Rain to complete the serum. However, Dr. Bouchard was killed by the Chimera. All surviving human personnel and refugees fled to Reims.
Following the evacuation to Reims, plans for the assault on the Paris tower were laid: Cartwright would lead the combined human military forces into battle on the Paris defenses and the tower. However, their goal is not only to destroy the hub tower, but also to distract the Chimera while allowing a small infiltration team into the city through the Paris catacombs and to the Chrysalis Lair, a conversion facility where Chimera DNA are implanted into captured humans before they are taken to other conversion facilities, and injecting Dr. Bouchard's serum into the facility's systems and thus contaminating the Chimeran conversion process and brought to a halt. Raine Bouchard volunteered for the infiltration due to her experience and knowledge of deploying the serum. But Raine was in fact already infected with the Chimeran virus and showing signs of falling to the Chimera's influence. James Grayson, having discovered Bouchard's infection, attempted to warn the Maquis and the British about Bouchard, but only to be refuted by Mallery and imprisoned for treason.
Fortunately, Grayson was freed by Cartwright and Rachel Parker and given a second sample of the serum to take to the Chrysalis Lair. At the same time Cartwright's forces engaged the Chimera in the city and suffering a grave amount of human casualties. Grayson encountered Mallery, who had became infected with the Chimeran virus and purposefully preventing Grayson from reaching the facility. Grayson killed Mallery and continued into the Chrysalis Lair, where he succeeded in deploying the serum just as Cartwright's forces destroyed the Paris tower. Just after Grayson used the serum, he discovered that Bouchard had mutated into a Chimeran entity calling itself the Chrysalis in which he engaged it in battle and finally ending what remained of Bouchard.
Operation Overstrike resulted in a major victory for humanity. Just as similar to the tower that fell in London, the destruction of the Chimeran tower in Paris led to the destruction of the tower network in Western Europe and causing all Chimeran forces stationed there to become disorganized, confused, and eventually dying out en masse. Poland, Spain, the Balkans, and Russia were still occupied by the Chimera, but after Overstrike these countries became the main battlefields in Northern, Eastern and Southern Europe.
The Carrier strains were eradicated by Claude Bouchard's serum, as the Carriers spread the contaminated fluid from the Chrysalis Lair to facilities all over France and Germany, and grounding the conversion process to a halt. However, the serum was only a temporary measure. The Chimera were able to overcome their setback by evolving and creating new strains among their ranks. Among them that succeeded the Carriers was the Spinner strain. Furthermore, the Chimera finished the construction of a vast fleet of airships with their targets and destinations unknown at the time. On September 9, the British and Maquis built a memorial for those who died in the war in Europe, and Grayson was promoted to Major.
- In Resistance: The Gathering Storm, Daedalus was looking through the eyes of other Chimeran species, in which he looked through the eyes of a Steelhead eating a human leg in Paris even though earlier Noah Grace was congratulating Stephen Cartwright for freeing western Europe. This can either be a mistake by the author or the Chimera trying to retake their lost territories like in Bracknell and Axbridge depicted in Resistance 2.
- ^ Radio-Free Rotterdam
- ^ In Retribution Lost, throughout the catacombs in Paris and the Chrysalis Lair, the player can occasionally hear orders from Cartwright towards his troops. He mentions that this diversion will not last forever due to heavy casualties, and hopes that Grayson has already made it through Paris.